When astronomers were first able to make detailed three-dimensional maps of distant galaxies, they were surprised to find that the galaxies in our universe are not distributed randomly, but instead gather into sheets and filaments. Cosmologists think that this large-scale structure arises from the growth of density variations, seeded by quantum mechanical fluctuations in the earliest moments of the birth of the universe. To test theories about the formation of large-scale structure, they run simulations of the evolution of our universe from the Big Bang to the present, using massive supercomputers.
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